US4612671A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Laser transmitter
Assignee: Nortel Networks Ltd
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Filing: 1984-10-29
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Granted: 1986-09-16
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Expires: 2004-10-29
Abstract
Abstract In a fiber optic laser controller for use in digital transmission a digital data stream and a DC bias are applied to the laser. During a monitoring period, the DC bias is stepped from a zero to a peak current. At a first threshold current, lasing occurs in response to digital `1` modulating current but not in response to digital `0` modulating current. At a second higher threshold current lasing occurs in response to both digital `1` and `0`. The threshold currents are identifiable as peaks in the second derivative d 2 L/dI 2 where L is the light output for an applied bias current I. A feedback circuit including a photodiode, D/A and A/D converters and a microprocessor controller are used to maintain the bias current at the second threshold current in spite of changes in the laser characteristics caused by device aging or temperature change.
Inventors
- 👤 Clinton R. Giles
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 19:29
CPC Classifications
H; H01; H01S; H01S5/00; H01S5/06; H01S5/068; H01S5/0683; H01S5/06835; H04; H04B; H04B10/00; H04B10/50; H04B10/501; H04B10/503; H04B10/504; H04B10/564; H01S5/06812; H01S5/06832
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
163 words
A laser controller for use in a digital transmission system, the controller comprising: means for applying a bias current to the laser; means for increasing the bias current from a low value below laser threshold to a high value above laser threshold; means for applying a digital data stream to the laser; means for monitoring laser light output power; means for storing monitored light output data (L) as a function of bias current data (I); means for processing the stored data: (i) to derive a second derivative d 2 L/dI 2 of the L-I curve; (ii) to find first and second peaks in the derivative, the first peak at a bias current I 1 th corresponding to a lowest bias current at which digital `1` but not `0` produces lasing and the second peak corresponding to the lowest bias current I 0 th at which digital `0` produces lasing; and means for setting the bias current at or close to I 0 th.
Claim 2
Dependent Claim
163 words
A laser controller for use in a digital transmission system, the controller comprising: means for applying a bias current to the laser; means for increasing the bias current from a low value below laser threshold to a high value above laser threshold; means for applying a digital data stream to the laser; means for monitoring laser light output power; means for storing monitored light output data (L) as a function of bias current data (I); means for processing the stored data: (i) to derive a second derivative d 2 L/dI 2 of the L-I curve; (ii) to find first and second peaks in the derivative, the first peak at a bias current I 1 th corresponding to a lowest bias current at which digital `1` but not `0` produces lasing and the second peak corresponding to the lowest bias current I 0 th at which digital `0` produces lasing; and means for setting the bias current at or close to I 0 th.
Claim 3
Dependent Claim
28 words
A laser controller as claimed in claim 1 in which the means for applying a bias current includes a microprocessor controller, a D/A converter and a filter element.
Claim 4
Dependent Claim
35 words
A laser controller as claimed in claim 2 in which the means for increasing the bias current includes a sub-routine in the microprocessor controller operating to change the D/A converter output in equispaced current intervals.
Claim 5
Dependent Claim
49 words
A laser controller as claimed in claim 1 in which the means for monitoring laser light output power includes a photodiode positioned to receive light from a reverse facet of the laser, primary laser output light being directed from a front facet of the laser into an optical waveguide.
Claim 6
Dependent Claim
35 words
A laser controller as claimed in claim 4 in which the means for monitoring light output power further includes an A/D converter having an input from the photodiode and an output to a microprocessor controller.
Claim 7
Dependent Claim
32 words
A laser controller as claimed in claim 5 in which the means for storing monitored light output (L) data and bias current (I) data is a memory section within the microprocessor controller.
Claim 8
Dependent Claim
58 words
A laser controller as claimed in claim 3 in which means for setting the bias current at or close to I 0 th is a further sub-routine in the microprocessor controller operating to set the output of the D/A converter in response to an input to the microprocessor controller from the means for monitoring laser light output power.
Claim 9
Dependent Claim
55 words
A laser controller as claimed in claim 1 further including a comparator for comparing data corresponding to average monitored light output level to data representing a desired average light output level, and means for adjusting the peak-to-peak level of the applied digital data stream to set the average monitored light output to said desired level.
Claim 10
Independent Claim
141 words
A method of controlling a semiconductor laser for use in digital transmission systems, the method comprising: applying a bias current to the laser; increasing the bias current from a low value below laser threshold to a high value above laser threshold; applying a digital data stream to the laser; monitoring laser light output power; storing monitored light output data (L) as a function of bias current data (I); processing the stored data: (i) to derive a second derivative d 2 L/dI 2 of the L-I curve; (ii) to find first and second peaks in the derivative, the first peak at a bias current I 1 th corresponding to a lowest bias current at which digital `1` but not `0` produces lasing and the second peak corresponding to the lowest bias current I 0 th at which digital `0` produces lasing; and
Claim 11
Independent Claim
141 words
A method of controlling a semiconductor laser for use in digital transmission systems, the method comprising: applying a bias current to the laser; increasing the bias current from a low value below laser threshold to a high value above laser threshold; applying a digital data stream to the laser; monitoring laser light output power; storing monitored light output data (L) as a function of bias current data (I); processing the stored data: (i) to derive a second derivative d 2 L/dI 2 of the L-I curve; (ii) to find first and second peaks in the derivative, the first peak at a bias current I 1 th corresponding to a lowest bias current at which digital `1` but not `0` produces lasing and the second peak corresponding to the lowest bias current I 0 th at which digital `0` produces lasing; and
Claim 12
Dependent Claim
11 words
setting the bias current at or close to I 0 th.
Claim 13
Dependent Claim
11 words
setting the bias current at or close to I 0 th.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1989-09-15 | 1990-03-17 | 1990-09-16 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-09-15 | 1994-03-17 | 1994-09-16 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-09-15 | 1998-03-17 | 1998-09-16 | $7700.00 | Window Closed / Lapsed |